To adjust the transmission ratio, continuously variable transmissions (CVTs) comprise a variator, usually with a pair of conical pulley discs respectively on the drive input and drive output shafts of the variator. Between this pair of conical pulley discs runs a belt, chain or jointed band looped around the drive input and output shafts. Each pair of conical pulley discs consists of a first conical pulley disc firmly attached to a shaft and a second conical pulley disc that can move in the axial direction. A mechanical or hydraulic actuation device is used to vary the axial position of the second, movable disc and hence also the effective diameter of the belt means for the continuous adjustment of the variator's transmission ratio.
From DE 38 16 357 C1 a continuously variable conical pulley and belt transmission system is known, in which a movable conical pulley disc of a variator represented therein is mounted on loose ball-bearings. These ball-bearings are guided in bearing races which are fitted, in the axial direction, on a variator shaft and the shank of the movable conical pulley disc. The variator shaft and the conical pulley shank have several such ball races. Two securing elements form the left and right abutments for the ball-bearings, which can move freely in the axial direction between the said abutments. During assembly of the pair of conical pulley discs, the security elements and the ball-bearings have to be fitted on individually by means of a device or by hand, which is troublesome and time-consuming.
To simplify the assembly of such a bearing for the movable conical pulley disc of a variator, EP 0 683 876 B1 proposes embedding the ball-bearings associated with one ball race in a holder element. The holder elements are designed such that the guiding function of the centering diameter between the movable conical pulley and the variator shaft is not compromised. The holder elements are at most connected to one another in a narrow area by means of a connector element. This makes it possible to fit all the ball-bearings in only one working step. Such holder elements and connector elements are usually made of sheet or plastic. To identify ball-bearings of the same tolerance the holder elements can be color coded.
From EP 0 957 295 A2 a belt-type variator is known, in which two bearing rings, by means of which the conical pulley of the variator that moves in the axial direction is mounted, are pressed onto the variator shaft that has the fixed conical pulley. When the transmission ratio is adjusted, the moving conical pulley slides axially on those bearing rings which therefore assume the function of a slide bearing. No additional element is provided for reinforcing the torque transfer of the moving conical pulley to the variator shaft. Because of this, the moving conical pulley can only transfer torque by friction force to the variator shaft, in other words by friction locking as a result of tilting of the moving conical pulley on the bearing rings. The torque transfer from the belt means to the variator shaft, therefore, takes place mainly via the fixed conical pulley disc.
Finally, from DE 195 44 644 A1 a variator for a continuously variable transmission is known in which a conical pulley, that can move in the axial direction, is mounted via two cylindrical sections of different diameter on a variator shaft having a fixed conical pulley, with no additional bearing elements. To reinforce the torque transfer of the movable conical pulley to the variator shaft, a splined shaft profile is provided between the conical pulley and the shaft which, for the purpose of torque transfer, must always have a minimum overlap and must have a certain clearance between the teeth to enable axial adjustability. To avoid wear, the splined shaft profile must be well supplied with lubricating oil at all times.
The purpose of the present invention is to provide a device in a continuously variable transmission system for guiding an axially movable conical pulley disc of a variator, on a variator shaft having a fixed conical pulley, the said device being inexpensive to manufacture and simple to assemble, and ensuring reliable torque transmission between the axially movable conical pulley disc and the variator shaft.
This objective is achieved by a device having the characteristics of the principal claim. Other advantageous features of the invention are defined in the subordinate claims.